The instant invention relates to a filter for a fluid medium, in particular oil, water, fuel or air filter for an internal combustion engine, comprising a filter housing and a cover, which is releasably connectable to the latter, comprising a replaceable filter insert, which consists of a hollow-cylindrical filter cloth body and two end discs, enclosing the latter frontally, the one end disc of which encompasses a central through hole, wherein, leading with the open end disc, the filter insert can be plugged onto a central stand pipe, which forms part of the filter housing, wherein a locking ring is guided in an axially displaceable manner on the stand pipe, wherein the locking ring is preloaded by a force acting in a pushed-out direction pointing towards the free end of the stand pipe, wherein, in a pushed-out position, the locking ring is locked by a locking device against being pushed in, wherein provision is made for unlocking means, which are guided by the filter insert and which, when the filter insert is pushed onto the stand pipe, actuate the locking device in the unlocking direction and enable the locking ring and the filter insert to be pushed in, and wherein, when the filter insert is fitted into the filter housing, a seal provided on the end disc or on the locking ring interacts with a sealing surface of the filter housing to separate an untreated medium side from a clean medium side of the filter. The invention furthermore relates to a filter insert for use in the above-mentioned filter.
Increasingly higher demands are made on filters, in particular oil, water, fuel or air filters for an internal combustion engine, in particular in view of the filter refinement and the service life of the replaceable filter inserts. These high demands can only be fulfilled, when suitable high-quality filter inserts are fitted into the filters.
A filter, by means of which the installation of an unsuitable third-party filter insert within the context of a filter maintenance with a filter insert replacement is interrupted, is known from EP 1 235 624 B 1. This document describes a filter comprising the above-mentioned features. The locking ring, which is guided on the stand pipe, is also a valve sleeve, which can be displaced axially on the stand pipe and which is preloaded with a force, which acts in valve closing direction. In the closed position of the valve, the locking ring latches with the stand pipe by means of locking lugs, which face radially inward, on locking tabs. By attaching a filter insert by means of suitable unlocking means, the latching of the locking ring or of the valve sleeve, respectively, with the stand pipe, is released, in that the locking tabs are pivoted radially outwardly. The locking ring is then displaced by means of the filter insert into valve open position and is held therein. An unsuitable third-party filter insert does not disengage the latching of the locking ring on the stand pipe and the filter insert cannot be attached completely onto the stand pipe. An operation of the filter is thus not possible, due to the valve body, which is in closed position; the same applies when a filter insert is missing. The locking ring is sealed against the stand pipe by means of a sealing ring. The end disc of the filter insert, which interacts with the locking ring, is sealed against the locking ring via a further sealing ring on the end disc.
Even though this known filter fulfills the demands of preventing the installation of an unsuitable third-party filter insert, a filter insert comprising an end disc comprising unlocking means, which are designed so as to be relatively extensive, is necessary for this purpose and two sealing locations, in each case comprising a sealing ring, are present, which is associated with an increased parts and assembly effort in a disadvantageous manner.